Topic Contents

Lactic Acid

Test Overview

A lactic acid test is a blood test that
measures the level of lactic acid made in the body. Most of it is made by
muscle tissue and
red blood cells. When the oxygen level in the body is
normal,
carbohydrate breaks down into water and carbon
dioxide. When the oxygen level is low, carbohydrate breaks down for energy and
makes lactic acid.

Lactic acid levels get higher when strenuous
exercise or other conditions—such as
heart failure, a severe infection (sepsis), or
shock—lower the flow of blood and oxygen throughout
the body. Lactic acid levels can also get higher when the liver is severely
damaged or diseased, because the liver normally breaks down lactic acid.

Very high levels of lactic acid cause a serious, sometimes
life-threatening condition called lactic acidosis. Lactic acidosis can also
occur in a person who takes metformin (Glucophage) to control
diabetes when heart or kidney failure or a severe
infection is also present.

A lactic acid test is generally done on
a blood sample taken from a vein in the arm but it may also be done on a sample
of blood taken from an artery (arterial blood gas).

How To Prepare

Do not eat or drink anything other than water
for 8 to 10 hours before the test.

Do not exercise for several hours before the test. Do not clench
your fist while having your blood drawn for a lactic acid test. These
activities may change the results.

How It Is Done

The health professional drawing blood
will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein. An elastic band may not be used for a
lactic acid test because a band around the arm muscle may cause a false
increase in lactic acid.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure on the site and then put on a
bandage.

How It Feels

The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.

Risks

There is very little chance of a problem from
having a blood sample taken from a vein.

You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.

Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (such as Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.

Results

A lactic acid test is a blood test that
measures the level of lactic acid made in the body. Most of it is made by
muscle tissue and
red blood cells.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Some medicines, such
as isoniazid for
tuberculosis or metformin (Glucophage) for
diabetes. Lactic acidosis is a concern for people who
take metformin to control their diabetes, especially if they have poor kidney
function.

What Affects the Test

Reasons you may not be able to
have the test or why the results may not be helpful include:

Taking large doses of the medicine
epinephrine.

Taking medicines, such as isoniazid for tuberculosis
or metformin (Glucophage) for diabetes.

Using a lot of
acetaminophen (such as Tylenol) or alcohol.

Exercising prior to
this test.

Clenching a fist while the blood sample is being drawn.
Also, lactic acid levels may be higher if the tourniquet is around your arm for
a long time.

What To Think About

Results from a lactic acid test may be more
accurate when the blood is taken from an artery (arterial blood gas) rather than from a vein. To learn more, see the topic
Arterial Blood Gas.

During aerobic
exercise, the heart and lungs supply adequate amounts of oxygen to the body for
energy. Anaerobic exercise uses more oxygen than the lungs and heart can supply
to the body so the energy supply is less, thus causing high lactic acid levels
in the blood. Usually anaerobic exercise forces a person to slow down or stop
exercising because lactic acid buildup causes moderate to severe muscle aches
and muscle stiffness. But some highly trained athletes learn to tolerate short
periods of high lactic acid levels. During aerobic exercise, the air you
breathe contains enough oxygen to use blood sugars normally and completely for
the body's energy needs, and lactic acid levels do not rise.

Lactic
acid can be measured in fluids other than blood, such as spinal fluid. Lactic
acid levels in body fluids often increase when an infection is present. The
amount of lactic acid in spinal fluid may be measured to determine whether a
brain infection is being caused by bacteria or a virus.

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